While running dropIndex command:
1- We acquire the lock of the collection using namespace.
2- We take a copy of the collectionUUID & the namespace.
3- We release the lock of the collection because of (SERVER-46216).
4- We reacquire the lock of the collection using db and collectionUUID.
5- after that we hit some code paths that assert that the locks for the namespace should be acquired.

The issue happens when there is a concurrent renaming happening, so the namespace of the collection can be changed between step 3 & 4, so any code path that checks for the locks for the old namespace will fail.

Suggestions: 
1- To update the local copy of the namespace of the collection each time we reacquire the lock on step 4.

2- (Harder) to make sure that after we release the lock on step 3, we don't use the namespace and replace it with db & uuid.